1. Field of the Invention
This invention relates to the refining of molten metal. More particularly, it relates to the lining of an aluminum or other molten metal refining vessel.
2. Description of the Invention
In the refining of aluminum, the prior use of externally heated, refractory lined cast iron tubs as refining vessels has been found to be disadvantaged by the limited and somewhat unpredictable life of such tubs. This undesired condition results from the failure of the cast iron tubs because of cracking, bulging, chloride corrosion or wash-out. In addition, design constraints pertaining to such cast iron tubs result in the use of vessel configurations that are difficult to clean, creating a further practical disadvantage to their use in commercial operations.
In an effort to overcome such disadvantages, refining systems were devised consisting of refractory lined vessels having electrical heating elements positioned in graphite blocks. Such systems comprised vessels adapted for the holding of aluminum in a molten state and including a shell having an inner refractory lining impervious to molten metal, with a lining comprising graphite blocks for a portion of the interior of the shell that is intended to be below the surface of the melt, and at least one electrical heating means disposed within one or more of the graphite blocks.
In the construction of a conventional all-refractory molten aluminum furnace or holding vessel, the vessel is usually lined with dense castable refractory or with dense refractory bricks. This material is not infiltrated by molten aluminum because it is too dense and contains only a small amount of porosity in the form of isolated bubbles and the like. The dense lining is backed up with a low density refractory insulating material which, in turn, is contained within a steel shell.
A common practice used to build or reline a conventional aluminum refining furnace involves pouring a castable refractory into the insulation-lined steel shell. The cast refractory must then be dried and cured in-situ by a lengthy process of heating the assembly in an oven or by the use of radiant heaters positioned inside the furnace.
In order to overcome the limitations of such in-situ casting approach, a pre-fired inner refractory lining has been inserted into a steel furnace shell lined with insulation. This approach requires less time than the casting and in-situ dryout procedure. Nevertheless, it still requires that a spent furnace be removed from its operating location, and lifted by a crane or other such device in order to dump the refractory lining material and repair or replace the refractory insulation of the stripped shell before insertion of the replacement preformed refractory lining.
There is a genuine desire and need in the art to develop an improved refractory lining for molten aluminum refining vessels and other such molten metal holding vessels. In particular, there is a need for lining structures that simplify the procedure for furnace lining, so as to preclude the need for removal of a spent furnace from its operational location and minimize the period of time in which the furnace is out of service.
With these and other objects in mind, the invention is hereinafter described in detail, the novel features thereof being particularly pointed out in the appended claims.